By Paul Waldrop, Principal Engineer, PacifiCorp
In the mid-1980s the power industry experienced high energy piping (HEP) system failures that resulted in personnel injuries and fatalities, as well as damaged equipment and loss of power generation. Power industry leaders worked together with the Electric Power Research Institute (EPRI) and the Materials Property Council (MPC) to study HEP failures, to understand the causes and to develop resources for avoiding future failures.
At that time, experience revealed that construction code criteria and available applications of non-destructive testing methods (NDE) could not provide relevant information regarding failure mechanisms. After extensive research the service damage mechanisms were discovered and documented. Additionally, it was observed that some of the underlying root causes of service damage could not be identified, resulting in an inability to accurately predict which components, welds or locations would experience accelerate service damage. Eventually, advanced NDE methods and metallurgical techniques were developed that provided relevant information.
As the power industry gained a better understanding of service damage, new NDE techniques and engineering tools were developed, yet some organizations continued to struggle to ensure communication, education and implementation of best industry practices.
PacifiCorp HEP Management
PacifiCorp has actively managed HEP since the mid-1980s. In 2007, PacifiCorp renewed its commitment to effectively manage HEP. Leadership within the organization envisioned a fully integrated and comprehensive HEP management and inspection program coupled with sound planning and budgeting processes. The vision was that the improved HEP program would be developed similarly to the PacifiCorp’s boiler tube failure reduction program (BTFRP), which was developed in accordance with EPRI recommendations.
The foundation of PacifiCorp’s new HEP program is a document entitled “The PacifiCorp High Energy Piping Safety and Reliability Program” (HEP S&RP). This document clarifies the overall intent of the improved HEP program. HEP S&RP has five sections which include purpose, overview, scope, standard practices and goals. HEP S&RP is critical in defining and documenting functions, actions, schedules and expected outcomes.
PacifiCorp’s values are integrally expressed in each section of the program document. The HEP S&RP was written from a senior management perspective. This document must be brief, clear and presented as a corporate directive. The program is approved by the vice president of generation.
The Overview section is a brief description of consequences of HEP failures and the increasing likelihood of HEP failures as a unit accumulates service hours. This section also states PacifiCorp’s determination to implement sound engineering judgment and best industry practices.
The Scope section facilitates creating a fully comprehensive and integrated HEP program. Most of the information presented concerning HEP failures is published with either a system approach or a single damage mechanism focus. PacifiCorp approached HEP management by first identifying the known service damage mechanisms and then defining and categorizing the systems affected by the particular service damage mechanism. The the categories and service damage mechanisms identified are Creep Affected Systems, Corrosion Fatigue and Fatigue Affected Systems and Flow-Accelerated Corrosion Affected Systems.
The Standards Practices section of the HEP S&RP consists of four subsections, one for each of the service- damage mechanisms, and a fourth providing direction for the development of the unit-specific HEP management and inspection plans (M &IPs). Each subsection provides a basic outline, general directions and identifies responsible individuals.
The Goals section is the last section in the HEP S&RP. PacifiCorp sets a high value on safety. This is reflected in PacifiCorp’s setting the prime HEP goal as “zero injuries due to HEP failure.”
As defined in the HEP S&RP, the next vital program document is “The Unit-Specific Management and Inspection Plan” (M&IP), which is organized into four sections. The first is an introduction section, which provides an in-depth explanation of each of the service damage mechanisms. The other three sections cover each of the three service damage mechanisms and the systems affected.
The M&IP is tailored to each unit and is the repository for all information that assists HEP engineers in developing recommendations and managing the Unit’s HEP. Each system is described in detail as to fabricator, material type, sizes and lengths. The type, number and location of welds are also documented. Additionally, drawings, specifications and operating conditions are referenced. The history of inspections, costs and man-hours expended for inspections of each system are incorporated. Also, included is a future scope of work and a supporting budget. The M&IP is approved by the plant’s managing director.
As a backup to the history section, PacifiCorp created an electronic library for each unit. A file naming nomenclature was created for ease of identification and to avoid duplication. The basic structure starts with capitalization of initials of the plant name, unit number, systems evaluated; the type of testing, the vendor and the year testing was performed.
The next three documents are attachments to the M&IP. They are the “Girth Weld Ranking Criticality Sheet,” the “Seam Weld and Location Ranking Criticality Sheet” and the “FAC Component Susceptibility Ranking Sheet.” These documents are designed as tools that assist engineers and managers in identifying locations, welds or components that are the most critical and cost effective to evaluate.
The ranking sheets are designed to help manage the risks of operating HEP by answering the question “which locations, welds or components should be evaluated next?” This is done by weighting all of the affecting parameters that influence HEP failures. The affecting parameters are then listed, including safety and cost, in a heading line. Each affecting parameter is then assigned a background color which corresponds to the applicable criteria and weight table of the same background color. Ranking sheets are updated each time new, more accurate data, or inspection results become available.
Implementing the Program
The setting of criteria and assigning of weights are the points where PacifiCorp’s goal and values are integrated into the process. The ranking sheets are designed such that weights are based on the number 4. PacifiCorp’s top goals are zero injuries and loss of generation due to HEP failures.
Examples of how PacifiCorp’s goals are incorporated is by assigning a factor of “2” to safety and only a factor of “1” to access (cost). Additionally, PacifiCorp assigned weights to the level of damage affecting parameter that initiates the desired action of repair or replacement well before failure. All the affecting parameters weights are summed and then averaged to produce a final score for a given location, weld or component.
In the case of FAC component susceptibility the ranking sheet is used as a guide for initial rankings. This sheet is similar to the EPRI ranking program CHECUP, in that it generally considers the various factors that affect FAC susceptibility. Because FAC affecting parameters are sometimes present in locations not expected, total and accurate prediction is nearly impossible.
For tools like the ranking sheets to be of value, the final ranking score must reflect carefully weighted affecting parameters. If an affecting parameter holds greater weight to the organization than another then the weighting factor should be adjusted accordingly. It should be kept in mind that assigning too high or too low a weighting factor to any one affecting parameter can skew the final score.
Criticality action levels (CALs) have been assigned to final scores. Assigning a CAL to the final score provides direction to the next appropriate action. The CALs are assigned as follows: A score of 6 or above requires immediate repair or replacement. A score between 5 and 5.99 requires repair or replacement during the next planned outage. These first two are assigned a CAL of “repair/replace” and are only implemented after metallurgical confirmation. A score between 4 and 4.99 requires evaluation or inspection at the next outage and is assigned a “high” CAL. A score between 3 and 3.99 is assigned a CAL of “medium.” A score between 0 and 2.99 is assigned a “low” CAL.
A benefit of the ranking sheets has been visual communication. As managers review the ranking sheets, they understand the interaction of the affecting parameters, weights, final scores and CALs. With the crucial information and the next best decision displayed in front of them, managers have assurance that all HEP issues are considered and confidence their decisions are enhancing plant safety.
Two additional attachments were created to facilitate communication with plant staff and vendors. The first spread sheet is “The Inspection Recommendations Sheet.” This tool identifies specific welds, locations or components to be evaluated and the appropriate NDE methods for each. The second spread sheet is the “Inspection Performance Tracking Sheet.” This spread sheet facilitates communication between plant management and contractors as preparations and inspections are completed.
Measure and Adjust
PacifiCorp revises the M&IP within six months of the last inspections and one year prior to the next inspections. During the first revision, a detailed scope of work and a budget for the next evaluations are developed. This revision provides ample time to secure funding and an opportunity to incorporate improvements and best industry practices. Reviewing the M&IP one year prior to the next inspections allows time for funding adjustments and the incorporation of any additional improvements, as well as re-familiarizing plant staff to the inspection plan and budget. This review also helps plant personnel integrate the HEP work activities into the overall plant scope of work, reducing or eliminating work interferences.
The standardized criteria and weights of the ranking sheets permit fleet-wide comparison of all HEP welds, locations or components. Once each HEP system is evaluated and characterized, only the welds that have a “high” CAL will be tracked for continuing service damage. The use of CALs provides direction to a point when the useful life of a location, weld or component has been sufficiently expended, yet can still operate safely and reliably while service damage is verified and if required repair or replacement plans and budgets are developed. These functions of the ranking sheets ensure HEP costs are at a minimum while securing safe and reliable operation.
A power company’s insurability, deductibles and pricing for boiler/machinery insurance are determined by risk ratings.
The PacifiCorp improved HEP program has been structured in such a way that it has broadened the understanding, knowledge, and support of the HEP program at all levels management and staff. With all pertinent information, data, and histories, documented in the M&IP, relatively little time is needed to familiarizing new personnel to the responsibilities and functions required to effectively manage HEP.